High-position-resolution neutron detector using a position-sensitive photomultiplier tube

Traditional neutron gas counters show limits when a spatial resolution under 1 millimeter in both directions is required. The detection of the light signal induced by a neutron interaction in solid scintillators allow to achieve a better spatial accuracy, but at the cost of a higher sensitivity to gamma-rays which represent the major source of noise in most of the neutron instruments. We have studied at the ELL a detector based on a Position Sensitive Photo-Multiplier Tube directly coupled to a scintillator, either GS20 Lithium glass(0.5mm and 1mm thick) or (LiF)-Li-6/ZnS : Ag (0.42mm thick) The simplicity of this device is very well suited when the position resolution is the main parameter of choice. These two types of scintillators are compared in term of energy spectrum, detection efficiency for thermal neutrons and for Co-60 gamma-rays, which, even if not representative of gamma environment on experimental sites allow this comparison. The counting rate limit is estimated from the light decay time and, position resolution, linearity and edge effects are discussed. We conclude that the GS20 scintillator give the best results, provided its thickness is properly choosen according to the wavelength of neutrons to be detected.